1. Field of the Invention
The present invention generally relates to a multi-layer ceramic module which utilizes discrete components such as decoupling capacitors and more specifically to an improved structure which reduces inductance effects associated with decoupling capacitors and which increases the effectiveness of decoupling capacitors.
2. Description of the Related Art
Advances in very large scale integration (VLSI) technology and increases in integration densities have caused numerous problems with multi-layer ceramic modules which utilize external discrete components in close proximity to the chip. As the size of the die or chip increased from a few millimeters to tens of millimeters, the on chip and off chip power distribution problem requires better power supply decoupling. The problem is somewhat relieved, especially for high frequencies, by on chip decoupling. However, for intermediate and low frequency decoupling one still needs to provide external decoupling capacitors as close as possible to the chip.
The conventional method of decoupling a module, or Temporary Chip Attach (TCA) substrate, is shown in FIG. 1. The decoupling capacitors 10 are typically placed on the top surface 11 of the MLC substrate 12 surrounding the chip 13 and are connected to internal MLC power and ground distribution planes. This method was conventionally adequate when the chips were relatively small in size and required low power, but with present day chips the distance from the edge of the chip to the center of the chip introduces significant distributed inductance which makes external decoupling highly ineffective.
In addition to power decoupling, it is often required to add external components to the MLC package in close proximity to the chip input/output. Such external components may consist of discrete passive RLCs or active chiplets with analog or digital functions. These external components are typically difficult to integrate in the integrated circuit and require low inductance, resistance, and cross coupling paths to the chip.
Furthermore, MLC substrates are often used as space transformers in state-of-the-art VLSI wafer test systems. The substrate is used in a "reverse" manner such that the pins of the module substrate interface with the test system's pin electronics test head, while the chip is replaced with the wafer contacting probe. One of the new probing approaches is to use Thin Film Interface (TFI) probes or membrane probes. However, a problem occurs because physically adapting these TFI probes to a MLC space transformer with decoupling capacitors on the periphery of the target area becomes somewhat difficult and costly.
The general problem of module package power supply decoupling is a well known problem and has been address before with a variety of configurations for different packages. However, none of the conventional solutions specifically address the problems of increasing chip size and TFI interfacing, described above.